1. Field of Invention
This invention relates to interconnection of digital integrated circuits and, more particularly, to reducing the number of input/output pins needed for communications and control between a plurality of digital integrated circuits.
2. Discussion of the Related Art
Semiconductor devices such as, for example, integrated circuits have revolutionized the field of electronics by making possible a level of technological sophistication unknown in the days of vacuum tubes and even discrete transistors. An integrated circuit die may comprise, on a small silicon chip, many thousand or even a million or more transistors interconnected together to form complex electronic functions. The complex electronic functions of the integrated circuit chip may require hundreds of external connections to a related electronic system.
Increases in electronic system performance, and the requirement to run complex computer software programs with a corresponding increase in memory requirements have dramatically increased the data throughput or "bandwidth" requirements of, for example, a computer system's memory and especially logic functions. At the same time, improvements in silicon integrated circuit technology have made it possible to integrate more and more logic functions onto a single integrated circuit chip. The advancements in technology and the corresponding utilization thereof have created the need for integrated circuit packages having input/output ("I/O") capacity requirements of over 500 external connections.
Simple function integrated circuits have been packaged in ceramic packages for high reliability industrial and military applications and in lower cost molded plastic packages for commercial and consumer products. Recently, very large scale integration (VLSI), ultra large scale integration ("ULSI"), and the like integrated circuits ("IC") have outgrown the connection capacity of either the ceramic or molded plastic packaging systems because of the large number of external connections required.
The IC packaging industry has therefore developed more sophisticated IC packages to accommodate the increased number of external connections required to be made to the associated electronic system. These IC packages, however, are expensive, difficult to fabricate, may require expensive sockets and take up a lot of valuable electronic system circuit board area. In addition, IC packaging technology has not been able to keep up with the rapidly increasing complexity and sophistication of integrated circuit technologies. This lag in IC packaging technology has limited the ability of the electronic circuit designer to utilize the full capabilities of present and future IC technologies in an easy to implement and cost effective way.
Another problem with IC packaging is the close proximity in spacing of signal connections that carry parallel data signals. Typically, parallel data signals may be digital words having 32, 64, 128 or more bits, and be connected to a parallel data bus having an equal number of conductive lands or wires such as a computer back plane or the like. The close proximity of many parallel signals having to drive a capacitive bus that may not be impedance matched creates signal crosstalk. Signal crosstalk further restricts the effective data rate and number of digital devices that may be effectively interconnected in an electronic system.
Yet another problem is connecting these parallel high bit capacity buses to the IC packages and then routing the physically wide parallel buses between the various IC packages on the electronic system substrate or printed circuit board. Sockets for the IC packages and connectors for peripheral printed circuit boards are expensive because of the large number of connections required. Similarly, leaded IC packages such as, for example, tape quad flat pack ("TQFP"), plastic quad flat pack ("PQFP"), and ball grid array ("BGA") packages require expensive equipment and complex procedures to accurately align the leads/balls on the substrate or board conductive land pattern.
As used herein, the term "semiconductor device" refers to a silicon chip or die containing electronic circuitry and is more commonly referred to as a "semiconductor integrated circuit" or "integrated circuit." The term "semiconductor device assembly" or "integrated circuit assembly" refers to the silicon die and associated packaging containing the die, including conductive leads, such as ball bump, pins, surface mount gull wing and J leads, conductive tabs or balls at the periphery of a package and/or on the interior of a surface or the like, for connecting to a system circuit board, and internal connections of the die to the conductive leads such as bond wires or tape automated bonding ("TAB"). The term "semiconductor device assembly" or "integrated circuit assembly" may also refer to the silicon die and associated leadframe such as a tape carrier or package-less silicon die on a leadframe which may be encapsulated or not. The leadframe is connected to the package-less silicon die as is well known to those skilled in the art of semiconductor devices.
What is needed is a method and system for reducing the required number of input-output pins necessary for communicating between complex integrated circuits that require high data throughput and are contained in simple and inexpensive integrated circuit assemblies.